In order to reduce aerodynamic drag, an air dam can be mounted forward of the front wheels of a motor vehicle. The dam also improves front end appearance of many vehicles by concealing the front end suspension and underside of the engine. The dam usually includes a central portion extending transverse of the body of the vehicle and a pair of wraparound corner portion that are longitudinal of the body. The corner portions may be separately molded from the central portion using a variety of plastics materials or together as a one-piece construction. In either case, the molder can select the characteristic of the plastics used in the molding to provide a light-weight panel at minimum costs. However, the strength of the dam is usually not great enough to withstand heavy impacts with low profile objects such as concrete parking bumpers, stops and the like, such bumpers being typically encountered in parking lots surrounding shopping malls and the like.
In U.S. Pat. No. 4,683,974 there is described an electromechanical switch having a switch contact that is mounted adjacent to the dam. As the dam is mechanically moved a preselected amount, the switch is closed placing a battery in circuit with a buzzer and a light. However, since activation is dependent upon mechanical movement of the dam, the correct installation and maintenance of such switches is essential and necessitate that actual contact occur between the structure to be protected and the object to be avoided.
In U.S. Pat. No. 4,352,090 there is shown a device in which an oscillator either oscillates or does not oscillate depending upon the capacitance between probes wherein obstacles to be avoided provide a dielectric effect or extended electrical ground and in that way a GO-NO GO alarm is controlled. However, since detection is dependent upon oscillator function, proper maintenance of the oscillator including calibration, is essential. Moreover, it would be desirable that the time interval after warning (but before actual impact between the dam and the object) be lengthened so that the operator of the vehicle can take evasive action.